Vehicle air conditioning circuit using a refrigerant fluid in the supercritical state

ABSTRACT

Refrigerant fluid such as CO 2 , compressed to the supercritical pressure by a compressor, is delivered selectively through a three-way valve, either into a branch of the circuit containing a cooler, an expansion device and an evaporator for cooling the cabin of a vehicle, or into a branch containing another expansion device and a heat exchanger for the purpose of heating the cabin.

FIELD OF THE INVENTION

[0001] This invention relates to air conditioning apparatus. Inparticular, the invention is directed to air conditioning apparatus,especially for the cabin of a vehicle, in which the apparatus includes:a first circuit branch for the flow of a refrigerant fluid therein, thefirst circuit branch containing a compressor which is arranged toreceive the refrigerant fluid in the gaseous state and to compress it toa supercritical pressure, and a second circuit branch containing a firstheat exchanger which is adapted to cool the fluid compressed by thecompressor at a substantially constant pressure, by transferring heatfrom a first external medium to the fluid; a first expansion devicewhich is adapted to reduce the pressure in the fluid leaving the firstheat exchanger, so as to put at least some of the fluid in the liquidstate; and an evaporator which is arranged to change the state of thefluid received from the first expansion device from the gaseous to theliquid state at a substantially constant pressure, by taking heat from asecond external medium for the purpose of cooling the space (for examplethe cabin of a vehicle) which is to be air conditioned. The fluid thusvaporised is then aspirated by the compressor.

BACKGROUND OF THE INVENTION

[0002] Forms of apparatus of the above general type are described forexample in the specifications of International Patent Publication No.WO93/06423, U.S. Pat. No. 5,245,836 and U.S. Pat. No. 5,291,941. Therefrigerant fluid used in these apparatuses is typically carbon dioxide(CO₂).

[0003] Where it is not required to cool the air which is to be deliveredinto the cabin of a vehicle, but merely to heat it, it is usual to makeuse of the heat which is produced by the propulsion engine of thevehicle, for example by passing air in contact with a heating radiatorthrough which the engine coolant fluid flows. When the engine is cold,no heat can be drawn from it for the purpose of heating the cabin. Thisresults in a considerable delay before the cabin can be brought to therequired temperature, and is consequently detrimental to the comfort ofthe occupants of the vehicle. In some cases, the coolant liquid never,during the whole duration of a journey, reaches a high enoughtemperature to warm the occupants as they would wish.

[0004] In order to enable the cabin to be brought to the requiredtemperature more quickly, various supplementary devices may be used, inparticular those which involve the use of heaters or electricalradiators, but these are somewhat expensive.

DISCUSSION OF THE INVENTION

[0005] An object of the present invention is to enable a space, forexample the cabin of a vehicle, to be heated more rapidly than hithertowhen the engine is cold, or to top up the quantity of heat where theheat available is insufficient, without the need to provide any costlyspecific means for this purpose.

[0006] According to the invention, an air conditioning apparatus,especially for the cabin of a vehicle, including for the flow of arefrigerant fluid therein, comprises a circuit having: a first circuitbranch which contains a compressor adapted to receive the said fluid inthe gaseous state and to compress it to a supercritical pressure, and asecond circuit branch containing a first heat exchanger arranged to coolthe fluid compressed by the compressor at a substantially constantpressure, by transferring heat to a first external medium; a firstexpansion device adapted to reduce the pressure of the fluid leaving thefirst heat exchanger so as to put at least some of this fluid into theliquid state; and an evaporator to put into the gaseous state the fluidderived in the liquid state from the first expansion device, at asubstantially constant pressure by taking heat from a second externalmedium for cooling the space to be air conditioned, with the fluid thusvaporised being subsequently aspirated by the compressor, ischaracterised in that the circuit further includes a third branch whichis disposed in parallel with the second branch and which contains asecond expansion device and a second heat exchanger, for transferringheat from the refrigerant fluid to the said second external medium so asto heat the said space, means being provided for causing the fluid toflow selectively in an air conditioning loop constituted by the saidfirst and second branches, or in a heating loop constituted by the saidfirst and third branches.

[0007] The second expansion device may be disposed either upstream ordownstream of the second heat exchanger.

[0008] A first pressure sensor is preferably disposed in the firstbranch, downstream of the compressor.

[0009] A second pressure sensor is preferably disposed in the secondbranch, between the first heat exchanger and the first expansion device.

[0010] A non-return valve is preferably disposed in the second branch,downstream of the evaporator.

[0011] According to a preferred feature of the invention, the circuitincludes at least one internal heat exchanger which is adapted totransfer heat between one section of the first branch, situateddownstream of the compressor, and either a section of the second branchsituated between the first heat exchanger and the first expansiondevice, or a section of the third branch which is situated upstream ofthe second heat exchanger.

[0012] In some embodiments of the invention, the above mentionedsections of the first, second and third branches may contain,respectively, the three heat exchanger elements of a three-way internalheat exchanger.

[0013] In other embodiments, the said sections of the first and secondbranches contain respectively the two ways, or heat exchanger elements,of a two-way internal heat exchanger, while the said sections of thefirst and third branches contain respectively the two ways, or heatexchanger elements, of a two-way second internal heat exchanger.

[0014] The said section of the third branch may be situated eitherdownstream or upstream of the second expansion device.

[0015] A third expansion device is preferably disposed in the thirdbranch upstream of the said section of the third branch.

[0016] The said section of the second branch is situated upstream of thesecond pressure sensor, where the latter is provided.

[0017] The said second external medium is preferably a stream of airwhich is then passed into the space such as the cabin of the vehicle.

[0018] The evaporator and the second heat exchanger are disposed inseries, in that order, in the path of the said stream of air inpreferred arrangements.

[0019] A heat source external to the refrigerant fluid circuit ispreferably disposed in the path of the said stream of air. It may bedisposed in this path downstream of the second heat exchanger, orbetween the evaporator and the second heat exchanger.

[0020] Means are preferably provided for varying the thermal powertransmitted from the second heat exchanger to the said second externalmedium. These power varying means may comprise means for adjusting thesecond expansion device and/or the third expansion device. They may,alternatively or in addition, comprise means for adjusting the capacityor speed of the compressor.

[0021] Preferably, a reservoir is disposed in the air conditioningcircuit upstream of the compressor.

[0022] The various features and advantages of the invention will appearmore clearly on a reading of the following detailed description of somepreferred embodiments of the invention, which are given by way ofnon-limiting example only and with reference to the accompanyingdrawings, in which those elements which are identical or similar to eachother are designated in all the Figures by the same reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIGS. 1 to 4 of the drawings are diagrammatic representations,simplified where appropriate, showing four different versions of an airconditioning apparatus for the cabin of a motor vehicle, in accordancewith the invention. FIGS. 1 to 4 show, respectively, a first, a second,a third and a fourth embodiment of the invention, by way of example.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0024] In the present description, the expression “air conditioningapparatus” means an apparatus which enables the temperature in a space(such as the cabin of a vehicle) to be regulated, either by removingheat from that space or by putting heat into the space, according to therequirements of the user. Each of the embodiments of the apparatus shownin the drawings comprises a refrigerant fluid circuit which has threebranches 1, 2 and 3. The branches 1 and 2 constitute a so-called airconditioning loop which is used to extract heat from the cabin; thebranches 1 and 3 together constitute a heating loop whereby heat issupplied to the cabin. This circuit is arranged to enable the pressureof a refrigerant fluid, and especially carbon dioxide, to vary on eitherside of the critical pressure.

[0025] A brief description will first be given of the air conditioningloop, which is practically identical in the four versions shown in thedrawings, and which is known per se. This loop comprises a compressor 4,which in the examples shown is of a variable output type, though it willof course be understood that the compressor need not be of a variableoutput type. The compressor 4 is followed in the loop by an oilseparator 5, from which oil is delivered to the compressor through afeedback line 6 which includes an expansion device 7 for reducing fluidpressure. A heat exchanger 8 enables some of the heat produced by therefrigerant fluid during its compression in the compressor 4 to betransferred to a stream of air

[0026] Connected to the heat exchanger 8, downstream of the latter, is aheat exchanger element 9 of an internal heat exchanger E. This, in thisexample, is a three-way heat exchanger for supplementary cooling of thefluid, comprising heat exchanger elements 9, 15 and 24 in heat transferrelationship with each other. Connected in the circuit downstream of theheat exchanger element 9 is another expansion device 10, downstream ofwhich an evaporator 11 is connected in the circuit. A further stream ofair F2 is passed through the evaporator 11, after which this air isdelivered into the cabin of the vehicle. A non-return valve 12 isprovided at the outlet of the evaporator. From the outlet of theevaporator 11, the fluid is passed, via the valve 12, into a reservoir13, which has a liquid return line 14.

[0027] The reservoir 13 prevents refrigerant fluid in the liquid statefrom being introduced into the compressor 4. In addition, the reservoir13 provides a reserve of fluid which enables any variations in load, orfluid charge, in the refrigerant circuit, to be compensated for. Thereservoir 13 has a main outlet for refrigerant fluid in the gaseousstate, and this outlet is connected to the second heat exchanger element15 of the internal heat exchanger E. The fluid flows in the heatexchanger element 15 in contraflow with respect to the flow in theelement 9. From the heat exchanger element 15, the fluid returns to thecompressor 4.

[0028] Again in a manner known per se, a heating radiator 20, which isthe conventional radiator in which coolant fluid from the engine of thevehicle is cooled, is arranged downstream of the evaporator 11 in theair stream F2. The stream of air F2 is produced by a conventionalmotorised fan unit 21.

[0029] A three-way valve 22 is disposed in the air conditioning loop,between the oil separator 5 and the heat exchanger 8. The three-wayvalve 24 is arranged to be controllable in such a way as to deliver thecompressed refrigerant fluid into the branch3, which terminates at ajunction point 23 situated between the non-return valve 12 and thereservoir 13. The branch 1, i.e. the branch which is common to both theair conditioning and heating loops, extends from the junction point 23to the three-way valve 22 via the reservoir 13, the heat exchangeelement 15 of the internal heat exchanger E, the compressor 4 and theoil separator 5. The second branch 2 of the air conditioning loopextends from the three-way valve 22 to the junction point 23, via theheat exchanger 8, the heat exchange element 9 of the heat exchanger E,the expansion device 10, the evaporator 11 and the non-return valve 12.

[0030] In the embodiment shown in FIG. 1, in the three-way internal heatexchanger E, heat is transferable between the heat exchange element 15and either the second element 9 or the third heat exchange element 24,which is disposed in the second branch 3 of the heating loop. The fluidflows in the heat exchange element 24 in contraflow to that in theelement 15. Considering the branch 3 in the direction of flow of thefluid in it, the heat exchange element 24 is followed by an expansiondevice 25, downstream of which, still in the branch 3, is a further heatexchanger 26 which is in the path of the stream of air F2 between theevaporator 11 and the radiator 20. The refrigerant fluid outlet of theheat exchanger 26 is connected to the junction point 23.

[0031] As has been indicated above, the three-way valve 22 can becontrolled in such a way that it causes the refrigerant fluid to floweither in the branches 1 and 2, that is to say in the air conditioningloop, or in the branches 1 and 3, that is to say in the heating loop. Inthe former case, the circuit then functions in the known way for coolingthe cabin, while in the latter case heat is transferred from therefrigerant fluid to the stream or air F2 by the heat exchanger 26,thereby enabling the cabin to be heated.

[0032] Reference is now made to FIG. 2, in which the refrigerant fluidcircuit differs from that shown in FIG. 1 in that the expansion device25 in the branch 3 is replaced by two expansion devices 30 and 31, whichare connected respectively upstream of the third heat exchange element24 of the internal heat exchanger E, and downstream of the heatexchanger 26. In addition, the heating radiator 20 is interposed betweenthe evaporator 11 and the heat exchanger 26 in the path of the stream ofair F2, instead of being downstream of the heat exchanger 26.

[0033] Referring now to FIG. 3, the arrangement shown in this Figurediffers from that in FIG. 2 in that the third heat exchanger element 24of the heat exchanger E is omitted, but a second internal heat exchangerE′ is provided instead. The heat exchanger E′ is a two-way heatexchanger, the two elements 32 and 33 of which are arranged for heattransfer between them. The heat exchange element 32 is disposed in thebranch 1, between the heat exchange element 15 of the other internalheat exchanger E and the compressor 4. The other heat exchange element33 is disposed in the branch 3 in the same way as the element 24 in FIG.2, so that the fluid flows in it in contraflow to the fluid flowing inthe heat exchange element 32.

[0034] Reference is now made to FIG. 4, in which the circuit againincludes internal heat exchangers E and E′ similar to those in FIG. 3,together with an air circuit F2 similar to that in FIG. 1 and anexpansion device 30 similar to those in FIGS. 2 and 3. However, thisexpansion device 30 is the only one in the branch 3, the expansiondevice 31 being omitted.

[0035] In all the various embodiments shown in the drawings, a pressuresensor 40 is disposed in the branch 1, between the oil separator 5 andthe three-way valve 22. In FIGS. 1, 3 and 4, a second pressure sensor 41is disposed in the branch 2, between the heat exchange element 9 of theinternal heat exchanger E and the expansion device 10. The power in theair conditioning loop is able to be controlled by making use of thesensor 41 if it is present, or the sensor 40. The latter can be used inall cases for controlling the power in the heating loop. Control of theair conditioning loop can be carried out in a known way by acting on thecapacity or on the speed of the compressor 4, or by acting on theexpansion device 10 appropriately. In addition, control of the heatingloop is able to be carried out by acting on the capacity or speed of thecompressor or on the expansion device, or devices, 25, 30, 31.

[0036] The various circuits illustrated show only some examples of thenumerous possibilities which result from all the possible practicalcombinations of the features described, such as:

[0037] the presence of a single expansion device or two expansiondevices in the branch 3, and the position of the single expansion devicewith respect to the heat exchanger 26;

[0038] the presence or absence of a pressure sensor in the branch 2;

[0039] the use of a three-way internal heat exchanger or two two-wayheat exchangers; and/or

[0040] the disposition of the heating radiator either upstream ordownstream of the heat exchanger 26.

What is claimed is:
 1. Air conditioning apparatus for treating theatmosphere in a space in a vehicle, the apparatus comprising a circuitfor flow of a refrigerant fluid therein, the circuit comprising a firstcircuit branch and a second circuit branch connected with the firstcircuit branch, the circuit including: a compressor in the first circuitbranch, adapted to receive said fluid in a gaseous state and to compressthis fluid to a supercritical pressure; a first heat exchanger in thesecond circuit branch, disposed downstream of the compressor forreceiving said fluid compressed by the compressor and for cooling suchfluid at substantially constant pressure by transfer of heat therefromto a first external medium, said first heat exchanger having an inletand an outlet for the said fluid; a first expansion device for receivingsaid fluid from said first heat exchanger and for reducing the pressurein said fluid so as to liquefy at least part of said fluid; and anevaporator downstream of the said first expansion device, for receivingthe said fluid in the liquid state from the latter and for putting thesaid liquid into the gaseous state at substantially constant pressure bytaking heat from a second external medium to cool the said space, theevaporator having an inlet side and an outlet side; and means connectingthe outlet side of the evaporator with the compressor whereby fluidvaporised in the evaporator is received by the compressor, wherein thecircuit further comprises: a third circuit branch disposed in parallelwith the said second branch; a second expansion device in the said thirdbranch; a second heat exchanger in the third branch downstream of thesaid second expansion device, for transferring heat from the refrigerantfluid to the said second external medium to heat the said space; andfluid flow switching means connected in said first branch and connectedwith the second and third branches of the circuit for selectivelydirecting the said fluid to flow in either of two modes, namely a firstmode in which said fluid flows in the first and second branches, whichthereby constitute an air conditioning loop, and a second mode in whichsaid fluid flows in the first and third branches, which therebyconstitute a heating loop.
 2. Apparatus according to claim 1 , whereinthe second expansion device is disposed upstream of the second heatexchanger.
 3. Apparatus according to claim 1 , wherein the secondexpansion device is disposed downstream of the second heat exchanger. 4.Apparatus according to claim 1 , further including a first pressuresensor disposed in the said first branch downstream of the compressor.5. Apparatus according to claim 4 , further including a second pressuresensor disposed in the second branch between the first heat exchangerand the first expansion device.
 6. Apparatus according to claim 1 ,further including a non-return valve disposed in the second branchdownstream of the evaporator.
 7. Apparatus according to claim 1 ,further including at least one internal heat exchanger comprising atleast two heat transfer elements in heat transfer relationship with eachother, with at least one of the said heat transfer elements beingarranged in the said first branch of the circuit so as to constitute asection of the first branch upstream of the compressor, the other saidheat exchange elements constituting a section of the second branchsituated between the first heat exchanger and the first expansion deviceand, respectively, a section of the third branch situated upstream ofthe second heat exchanger, whereby the said at least one internal heatexchanger can transfer heat between the said section of the first branchand the said sections of the second and third branches.
 8. Apparatusaccording to claim 7 , wherein the said at least one internal heatexchanger comprises a three-way heat exchanger, each of the saidsections of the first, second and third branches constitutingrespectively a first, second and third heat exchanger element of thethree-way heat exchanger.
 9. Apparatus according to claim 7 , whereinthe said at least one internal heat exchanger comprise a two-way firstinternal heat exchanger and a two-way second internal heat exchanger,the first internal heat exchanger comprising two said heat exchangerelements in the said sections of the first and second branchesrespectively, and the second internal heat exchanger having two heatexchange elements in the said sections of the first and third branchesrespectively.
 10. Apparatus according to claim 7 , wherein the secondexpansion device is disposed upstream of the second heat exchanger, thesaid section of the third branch being situated downstream of the secondexpansion device.
 11. Apparatus according to claim 7 , wherein thesecond expansion device is disposed upstream of the second heatexchanger, the said section of the third branch being situated upstreamof the second expansion device.
 12. Apparatus according to claim 7 ,wherein the second expansion device is disposed downstream of the secondheat exchanger, the circuit further including a third expansion devicedisposed in the third branch, downstream of the said section of thethird branch.
 13. Apparatus according to claim 7 , further including afirst pressure sensor disposed in the first branch, downstream of thecompressor, and a second pressure sensor disposed in the second branchbetween the first heat exchanger and the first expansion device, thesaid section of the second branch being situated upstream of the secondpressure sensor.
 14. Apparatus according to claim 1 , further includingmeans for creating a stream of air for delivery into the said space anddefining a path for the said stream of air, the said stream of airconstituting the said second external medium.
 15. Apparatus according toclaim 14 , wherein the evaporator is disposed in the path of the saidstream of air, the second heat exchanger being disposed downstream ofthe evaporator in the said path.
 16. Apparatus according to claim 15 ,further including a heat source external to the refrigerant fluidcircuit and disposed in the path of the said stream of air downstream ofthe second heat exchanger.
 17. Apparatus according to claim 15 , furtherincluding a heat source external to the refrigerant fluid circuit anddisposed in the path of the said stream of air between the evaporatorand the second heat exchanger.
 18. Apparatus according to claim 1 ,further including means for varying the thermal power transmitted fromthe second heat exchanger to the said second external medium. 19.Apparatus according to claim 12 , further including power varying meansassociated with at least one of the second and third expansion devices,for adjusting the said at least one device whereby to vary the thermalpower transmitted from the second heat exchanger to the said secondexternal medium.
 20. Apparatus according to claim 18 , wherein the saidpower varying means comprise means associated with the compressor, foradjusting a parameter of the compressor selected from the groupconsisting of its capacity and its speed.
 21. Apparatus according toclaim 1 , further including a reservoir disposed in the refrigerantfluid circuit upstream of the compressor.